Which of the following is NOT a drug commonly used to treat muscle spasms?

The correct choice indicates that Tylenol is not a drug commonly used to treat muscle spasms. This is because Tylenol, or acetaminophen, primarily functions as an analgesic (pain reliever) and antipyretic (fever reducer). It does not have properties conducive to relaxing muscles or targeting muscle spasticity.

In contrast, Valium (diazepam) is a benzodiazepine that can help relax muscles by decreasing muscle tone and preventing spasms. Baclofen is specifically designed for the treatment of muscle spasms, particularly in conditions like multiple sclerosis or spinal cord injury. Dantrium (dantrolene) also directly acts on skeletal muscle to reduce spasticity and is commonly used for treating malignant hyperthermia and spasticity from neurological conditions.

This highlights Tylenol's role as a symptomatic pain reliever rather than a treatment for muscle spasms, distinguishing it from the other medications listed.